Slip-resistant thermoplastic resin sheets and process for producing same



Apnl 19, 1966 TE|HER 3,246,831

SLIP-RESISTANT THERMOPLASTIC RESIN SHEETS AND PROCESS FOR PRODUCING SAMEOriginal Filed Oct 19, 1961 COLLODEAL SILKCA-LATEX COATING THERMOPLASTICFILM '2 (5.0. POLYETHYLENE) FIG. I

INVENTOR HARRY TEICHER ATTORNEY United States Patent 3,246,831SLIP-RESISTANT THERMOPLASTIC RESIN SHEETS AND PROCESS FOR PRODUCBNG SAMEHarry Teicher, Olivette, M0., assignor to Monsanto Company, St. Louis,Mo., a corporation of Delaware Original application Oct. 19, 1961, Ser.No. 145,183. Divided and this appiication Jan. 11, 1965, Ser, No.424,677

5 Claims. (Cl. 229-53) The present application is a division of mycopending application, Serial No. 145,183, filed for Letters Patent inthe United States Patent Oflice October 19, 1961. The application SerialNo. 145,183 should be considered with the present application.

The present invention relates to treated or coated sheets or filmsfabricated from thermoplastic resins or polymers, and particularly totreated or coated sheets or films which have a slip-resistant surface.This invention also relates to methods of treating the surfaces ofnormally slippery thermoplastic resin or polymer sheets or films torender such surfaces slip-resistant. The present invention moreparticularly relates to treated or coated polyolefin sheets or filmswhich are characterized by a slip-resistant sur face, and to methods formaking polyolefin sheets or films slip-resistant. The present inventionalso relates to improved packaging containers fabricated fromthermoplastic resin sheets or films which containers are characterizedin having a slip-resistant surface.

Thermoplastic resins or polymers, particularly those which arewater-insoluble, such as polyvinyl acetate, polyvinyl chloride,polystyrene, polyethylene, polypropylene and mixtures thereof, amongothers, have been fabricated into a Wide variety of articles such asmolded containers, clocks, pipes, fibres, filaments and rigid andnon-rigid or flexible films or sheets, and have also been applied tocellulose paper or paperboard as a film or coating on these articles toprovide a water-resistant or water-vapor resistant barrier.Thermoplastic resin or polymer films and sheets have been in increasingquantities for such uses as covering materials, such as tarpaulins, aswell as in the packaging industry where such sheets and films havecertain distinct and well-known advantages (e.g. improved resistance tomoisture vapor transmission) over conventional cellulosic packagingmaterials such as, for example, paper or cellophane. However, sheets orfilms fabricated from such thermoplastic resins possess the inherentdisadvantage of having an extremely slippery surface which restrictstheir use in a number of applications. Thus, for example, when used as atarpaulin to cover machinery such films slip or are easily dislodgedfrom the machinery and although otherwise suitable for use as dropcloths for painters, the slippery surface of such materials constitutesa safety hazard. Also, when the films are fabricated into containerssuch as bags, the containers slip and slide against each other whenbeing transported by hand, truck, motor vehicles, rail carriers, watercarriers and the like, are difficult to store in stacks and often slidewhile in storage. This phenomena results in shifting of loads, spillage,loss of containers from moving ,vehicles and accidents to handling andwarehouse personnel.

Attempts which have been made heretofore to overcome the difliculty ofthe slippery surface of thermoplastic resin or polymer films, withoutotherwise adversely altering one or more such properties as flexibility,transparency, tensile strength, tear strength, printing char:acteristics and the like, have been largely unsuccessful.

" Novel, treated or coated thermoplastic resin sheets or films having aslip-resistant surface, the methods for treating the surfaces ofnormally slippery thermoplastic resin or polymer sheets or films andimproved packaging containers fabricated from thermoplastic resin sheetsand films and characterized in having a slip-resistant surface weredisclosed in my application for Letters Patent Serial No. 65,188, filedin the United States Patent Office, October 26, 1960, and assigned tothe same assignee as the present application. The disclosure containedin the present application should be taken in conjunction with saidapplication for Letters Patent Serial No. 65,188 and considered as acontinuation-in-part of said application Serial No. 65,188, nowabandoned, and as a division of the aforementioned application SerialNo. 145,183.

It is one object of the present invention to provide thermoplasticpolymer films and sheets which are characterized in having aslip-resistant surface.

It is another object of the present invention to provide a process fortreating thermoplastic polymer films and sheets to render themslip-resistant.

It is still a further object of the present invention to provideimproved slip-resistant packaging containers fabricated fromthermoplastic resins or polymers.

Other objects and advantages of the present invention will becomeapparent from the following description and the appended claims.

In the accompanying drawings, forming a part of this specification, andin which like numerals are employed to designate like parts throughoutthe same,

FIGURE 1 is a vertical section through a slip-resistant, coated ortreated thermoplastic film embodying the present invention, and

FIGURE 2 is a side elevation, partially in section, of a transparent,slip-resistant, coated or treated packaging container fabricated ofthermoplastic film and embodying the present invention.

The present invention is based on the unexpected discovery that theslippery surface of rigid, semi-rigid or flexible thermoplastic resinfilms or sheets, or cellulosic sheets having an outer coating or film ofsuch thermoplastic resin or polymer, thereon, can be renderedslipresistant when coated with a material comprising an aqueous medium,having dispersed therein an alkalistabilized colloidal silica and fineor colloidal particles of an inter-polymer or copolymer (preferablyderived from an aqueous latex containing such inter-polymer particles)comprising the inter-polymerization product of a monovinylidene aromatichydrocarbon, an alkyl ester of acrylic or methacrylic acid, and anethylenically unsaturated organic carboxylic compound having at leastone carboxyl group, for example, a copolymer latex con taining acopolymer of from about 26% to about 65% by weight of styrene, fromabout 60% to about 34.5% by weight of an alkyl acrylate and from 14 to0.5% by weight of an ethylenically unsaturated organic carboxyliccompound containing from 3 to 9 carbon atoms, having at least 1 carboxylgroup and copolymerizable therewith. The quantity of colloidal silica insuch compositions is usually in the range of about 8% to 30% of thecomposition and is also in the range of about 10 to 500 parts by weightper parts by weight of said copolymer in the composition. Suitableinterpolymers are comprised of from about 25% to 65 by weight of amonovinylidene aromatic hydrocarbon from about 60% to 34.5% by weight ofan alkyl acrylate or alkyl methacrylate and from about 15% to 0.5% byweight of an ethylenically unsaturated carboxylic compound having atleast one carboxyl group and copolymerizable with the monovinylidenearomatic hydrocarbon and alkyl acrylate or methacrylate.

Such interpolymer or copolymer may also include, chemically combined orcopolymerized therein in addi-- tion to the monomeric compoundsdescribed above, an'

unsaturated nitrile preferably a vinyl nitrile or vinylidene nit-rile.

When the interpolymer or copolymer contains an unsaturated nitrile, suchnitrile will generally replace a portion of the monovinylidene aromatichydrocarbon and/ or a portion of the alkyl ester of acrylic ormethacrylic acid and/or a portion of the ethylenically unsaturatedcarboxylic compound, but preferably replaces a portion of such alkylester and a portion of. such carboxylic compound.

Examples of such copolymers which have been found particularly suitableare copolymers of from about 25% to 60% by weight of monovinylidenearomatic hydrocarbon, preferably styrene, from about 60% to 35% byweight of an alkyl ester of acrylic or methacrylic acid, from to byweight of a copolymerizable ethyl enically unsaturated carboxyliccompound, having at least one carboxyl group and copolymerizable withthe styrene and the alkyl ester. of acrylic or methacrylic acid and fromabout 10% to about 3% by weight of an unsaturated nitrile, preferably avinyl or vinylidene nitrile.

In FIGURE 1 of the accompanying drawings, wherein for the purpose ofillustration is shown one preferred embodiment of this invention, thenumeral 10 designates an article of manufacture comprising a sheet 12 ofthermoplastic resin or polymer (preferably polyethylene) having a'thincontinuous coating 11 which is transparent and adherent to thethermoplastic sheet and is composed, for example, of a uniform mixtureof colloidal particles of the aforementioned alkali-stabilized colloidalsilica and interpolymer, for example, an interpolyrner of styrene, alkylacrylate and unsaturated carboxylic compound, preferably derived fromthe aforementioned latices. The coating 11 may be continuous ordiscontinuous but, in any event, provides slip-resistance to the coatedsurface of article 10.

The liquid coating compositions which form the coatings 11 prepared inaccordance with this invention are essentially composed of a continuouswater phase and a disperse phase comprising such colloidal silica andcolloidal particles of the aforementioned copolymers. The water phasemay have dissolved therein a dispersing or emulsifying agent and thecatalysts used in the preparation of the copolymers. When thesematerials are formed into a liquid film or coating on a thermoplasticresin film or sheet it is possible to dry such liquid film to provide aclear continuous or discontinuous transparent solid coating which willprovide a slip-resistant surface to the thermoplastic resin film.

The alkali-stabilized colloidal silica aquasols, which may be employedin the liquid coating compositions used in this invention, may beprepared in a variety of Wellknown ways. Thus such aquasols may beprepared from aqueous sodium silicate solutions by treatment withcation-exchange resins operating on the hydrogen cycle thereby reducingthe Na O to SiO ratio of the original sodium silicate solution andproviding a sol'having an SiO to Na o ratio in the range of about 10:1to 500:1. Such procedures are described in general and in greater detailin U.S. iPatent No. 2,244,325 to Paul C. Bird granted June 3, 1941; US.Patent No. 2,457,791 to Vandeveer Voorhees granted January 4, 1949; US.Patent No. 2,573,743, to Henry S. Trail granted November 6, 1951; US.Patent No. 2,574,902, to Max F. Bechtold and Omar E.'Snyder grantedNovember 13, 1951; and US. Patent No. 2,577,485 to Joseph M. Rulegranted December 4, 1951. Further, such silica sols may be prepared bydispersing silica hydrogels at elevate-d temperatures in the presence ofan aqueous solution of small amounts of sodium hydroxide or an alkalineheat stable aquasol, as described, for example, in US. Patent No.2,375,738 to John F. White granted May 8, 1945, and U.S. Patent No.2,572,578 to Henry S. Trail granted October 23, 1951, respectively.Moreover, the alkali-stabilized colloidal silica sols may be prepared byremoving the organic diluent from an alkaline organo-aquasol asdescribed in US. Patent No. 2,515,949 to Vincent Di Maio granted July18, 1950 or US. Patent No. 2,515,961 to Morris D. Marshall granted July18, 1950, or by alkalizing an acidic organo-aquasol and removing theorganic diluent therefrom as described in the aforesaid Di Maio andMarshall patents or as described in U.S. Patent No. 2,515,960 to MorrisD. Marshall granted July 18, 1950.

All of the silica aquasols; prepared by the procedures referred to .inthe preceding paragraph, may be used in the liquid coating compositionsherein described. All of these sols are slightly alkaline, having a pHin the range of 8.5 to 11.0, and have an SiO to M 0 mol ratio, where Mis an alkali metal, in the range of about 10:1 to 500: 1, and usually inthe range of about :1 to about 200:1 more desirably a range of about :1to about 300:1. These silica sols are also stable, in that they remainfluid, that is, do not gel for periods of about six months or longer at20 C. at silica concentrations of about 20% by weight. However,depending upon the particular procedure used, stable silica aquasolscontaining up to 45% by weight of silica can be prepared.

Silica aquasols containing from 5% to 45% by weight, preferably 15% to40%-by weight of colloidal silica,

may be generally used in the compositions of the present invention andsuch sols have an average ultimate particle size of less than about 250millimicrons and generally in the range of about 5 to 200 millimicrons.The preferred sols have average colloidal silica particles of a size inthe range of about 5 to 30 millimicrons, more particularly a range ofabout 10 to 25 millimicrons. When .it is desired to obtain transparentfilms from the compositions of this invention, it has been generallyfound desirable to employ silica sols in which the average particle sizeis below millimicrons preferably 5-80 millimicrons, since silica solscontaining larger average size particles tend to produce hazy or opaquefilms. Film transparency or opacity is also dependent on film thickness,that is thinner films are more transparent, all things being equal, thanthicker films. All of these sols contain essentially .no, or onlyrelatively small amounts, of water-soluble inorganic salts, usuallysodium sulfate or sodium chloride, or both, which originate from .theraw materials, for example, sodium silicate or sulfuric acid, employedin their manufacture. Usually such solswill contain less than 1.5% forexample, in the range of 0.2 to 1.5% by weight of such inorganic saltsand, in most instances, the sols prepared from sodium silicate andcation-exchange resins (for example, the process of the above Birdpatent) ,or by dispersing silica hydrogel (forexample, the process ofthe above White patent) will contain less than 1%, for example, in therange of 0.1 to 1% by weight of such inorganic salts.

The copolymers or interpolymers employed in the liquid coatingcompositions used in this invention are preferably derived from aqueouslatices which comprise extremely fine or colloidal particles of the low.molecular weight copolymers, hereinbefore defined, which dispersedcopolymer particles may vary somewhat asto particle size but desirablyhave a particle size in the range of about 50 to 8,000 Angstroms. Whenthe copolymers do not include an unsaturated;nitrile, the dispersedcopolymers preferably have a particle size :in the, range of centipoisesat 25 C. and a specific gravity betweeri10l When the co-' The copolymersor intcrpolymers may be prepared from styrene or a wide variety of othermonovinylidene aromatic hydrocarbons, including monomers such as alphamethyl styrene, parachlorostyrene, 2,4-dichlorostyrene,2,5-dichlorostyrene, parabromostyrene, paramethylstyrene,alphamethylparamethylstyrene, metaethylstyrene, para-isopropylstyrene,vinyl naphthalene and the like. Mixtures of two or more such compoundsmay be employed if desired. However, the preferred monovinylidenehydrocarbon is styrene.

The acrylic or methacrylic alkyl esters used in preparing the copolymersemployed in compositions of the present invention are alkyl acrylates ormethacrylates wherein the alkyl group has from 1 to 20 carbon atoms. Ofspecial utility, are alkyl acrylates or methacrylates wherein the alkylgroup has from 4 to 20 carbon atoms. The copolymers or interpolymerswhich are preferably employed in the compositions of this invention maybe prepared from a wide variety of acrylic and methacrylic alkyl estersincluding straight chain and branched chain aliphatic alcohols, andesters of these acids. Examples include those esters formed byesterifying acrylic or methacrylic acid with alcohols such as amylalcohol, hexanol, 2-ethyl hexanol, octanol, Z-methyl pentanol, the x0alcohol of isobutylene dimer, heptyl alcohol, 3-methyl heptyl alcohol,tridecyl alcohol, tetradecyl alcohol and the like. Mixtures of two ormore such acrylic or methacrylic acid esters may be employed if desired.

The preferred acrylic or methacrylic acid alkyl esters used in preparingthe copolymers employed in the compositions of the present invention,when the copolymers do not contain an unsaturated nitrile, are alkylacrylates, or methacrylates wherein the alkyl group has from 1 to 8carbon atoms. Of special utility are alkyl acrylates wherein the alkylgroup has from 4 to 8 carbon atoms and octyl acrylates is particularlypreferred.

When the copolymer is one which contains combined therein an unsaturatednitrile, the acrylic or methacrylic acid alkyl esters employedpreferably are alkyl acrylates or methacrylates wherein the alkyl grouphas from 5 to 20 carbon atoms and 2-ethylhexyl acrylate or methacrylateand decyl acrylate are particularly preferred.

A large variety of unsaturated organic compounds containing from 3 to 9carbon atoms and having at least one carboxyl group may be copolymerizedwith styrene or one of the other monovinylidene hydrocarbons and thealkyl acrylates in forming the aforedescribed interpolymer orcopolymers. A's exam-pies of such unsaturated organic carboxyliccompounds may be mentioned the ethylenically-unsaturated aliphaticmonocarboxylic acids such as alkenic monocarboxylic acids having from 3to 6 carbon atoms as, for example, acrylic acid, butenic acids such ascrotonic acid, isocrotonic acid, methyl acrylic acid and vinyla-ceticacid, and pentenic acids such as tiglic and angelic acids. In general,the ethylenically-unsaturated aliphatic monocarboxylic acids of thegeneral formula C H2 2O2, where n is a whole number of from 3 to 6 andwhich are copolymerizable with styrene or the other monovinylidenearomatic hydrocarbons and alkyl acrylates are useful in preparing suchcopolymers.

As further examples of such unsaturated organic compounds containingfrom 3 to 9 carbon atoms and having at least one carboxyl group may bementioned the ethylenically-unsaturated organic polybasic carboxylicacids such as maleic anhydride and maleic acid which are copolymerizablewith stryene or the other monovinylidene aromatic hydrocarbons and alkylacrylate monomer and also the relatively water-insoluble,ethylenically-unsaturated aliphatic dicarboxylic acids of which fumaricand itaconic acids are examples. Of these latter two fumaric acid ispreferred because it is available commercially.

As further examples of unsaturated organic carboxylic compoundscontaining from 3 to 9 carbon atoms and having at least 1 carboxyl groupmay be mentioned the partial esters of ethylenically-unsaturatedaliphatic dicarboxylic acids which are copolymerizable with styrene orthe other monovinylidene aromatic hydrocarbons and alkyl acrylatemonomers and preferably the alkyl half ester of such acids. As examples,of such partial esters may be mentioned the alkyl half esters of maleicacid in which the alkyl group contains from 1 to 4 carbon atoms, such asmethyl, ethyl and pr-opyl acid maleate; the alkyl half esters of fumaricacid in which the alkyl group contains from 1 to 4 carbon atoms such asmethyl acid fumarate and secondary butyl acid fumarate; the alkyl halfesters of citraconic acid, in which the alkyl group contains from 1 to 4carbon atoms such as methyl and butyl citraconates; alkyl half esters ofchloromaleic acid in which the alkyl group contains from 1 to 4 carbonatoms, such as ethyl and butyl acid chloromaleates; and alkyl halfesters of itaconic acid in which the alkyl group contains from 1 to 4carbon atoms, such as methyl and butyl acid itaconates and the like.These esters, with the exception of the alkyl acid itaconates arerepresented generally by the structural formula where X is hydrogen,halogen (prefer-ably chlorine) or an alkyl group having at most a numberof carbon atoms such that the total number of carbon atoms in the esterdoes not exceed 9, and where X; is the same as X or is preferablyhydrogen when X is other than hydrogen, and where R is an alkyl grouphaving 1 to 4 carbon atoms. It is to be understood that the foregoingstructural formula for the esters is intended to include the cisandtrans-forms of the esters. Of the above esters, the alkyl half esters ofmaleic acid are preferred because they are readily prepared fromcommercially available alcohols and commercially available maleicanhydride. Of these half esters, the methyl half ester of maleic acid ispreferred for preparing copolymers with styrene and alkyl acrylates foruse in the compositions which form the slip-resistant coatings used inthis inventi-on.

It is to be understood that the copolymers described herein may comprisestyrene, mixtures of alkyl acrylates, in which the alkyl groups havefrom 4 to 8 carbon atoms, and the unsaturated carboxylic compoundshereinbefore described, for example, copolymers of styrene, alkylacrylates having less than 9 carbon atoms, crotonic acid and alkyl halfesters of maleic acid in which the alkyl group contains between 1 and 4carbon atoms, copolymers of styrene, alkyl acrylates, crotonic acid,acrylic acid and the like.

When the copolymers employed in the compositions of this inventioninclude unsaturated nitriles it is preferred to use, as theethylenically unsaturated carboxyl containing comonomer, an unsaturatedmonocarboxylic acid including, for example, acrylic acid, methacrylicacid, cinnamic acid, cnotonic acid, atropic acid and the like. Theunsaturated nitriles which may be employed in the latices are vinyl orvinylidene nitriles and include acrylonitrile and methacrylonitrile. Amixture of unsaturated nitriles such as acryonitrile wit-hmethacrylonitrile or a mixture of two or more of the unsaturatedmonocarboxylic acids may also be used if desired.

The preferred copolymers of this invention (when the unsaturatednitriles are not incorporated therein) from the standpoint ofproportions of ingredients are copolymers of from 30% to 48% by weightof styrene or other monovinylidene aromatic hydrocarbons from 69.5 to38% by weight of alkyl acrylate or methacrylate and from 0.5% to 14% byweight of the unsaturated organic carboxylic compounds hereinbeforedescribed. When the above-described unsaturated nitriles areincorporated, the preferred proportions are from 40 to spanner 60% byweight of styrene or another monovinylidene aromatic hydrocarbon from 45to 35% by weight of alkyl acrylate or alkyl methacrylate, from to 2% ofthe ethylenically unsaturated organic monocarboxylic compound and fromto 3%-by weight of unsaturated nitrile. The preferred copolymers (whichdo not contain an unsaturated nitrile) of this invention from thestandpoint of molecular weight are copolymers which have amolecularweight such that an aqueous latex containing 40% by weight ofcopolymers in the form of discrete particles having a particle size inthe range of 150250 Angstroms, a specific gravity of 1.01 at C. and aviscosity (Brookfield) of between 600 and 800 centipoises at 25 C. Wherethe copolymer includes an unsaturated nitrile the particle size of thecopolymer particles preferably is in'the range of from about 1,000 to5,000 Angstroms, although the Specific gravity and viscosity will besubstantially the same as for the copolymers described in the precedingsentence.

The copolymer particles employed in the compositions used in thisinvention may be prepared by various processes well-known to thoseskilled in the art. In the examples, herein described such copolymerparticles were prepared in the form of an aqueous latex according to thefollowing procedure.

Three hundred seventy parts by weight of a mixture comprising 40% byweight of styrene, 58% by weight of octyl acrylate and 2% water areplaced in a suitable reactor equipped with agitator and a nitrogeninlet. There is also added 350 parts by weight of 2.2% aqueous solutionof sodium lauryl sulfate, 0.04 part by weight of FeSQ -9H O and 0.7 partby weight of hydrogenperoxide.

Reaction is initiated by stirring at a temperature of about C. to C.after sweeping out all of the air from the. apparatus and, once started,is allowed to proceed at a steady temperature of about 30 C. At the sametime, there is added steadily, at the rate of about 6 to 8 parts byweight per hour for 18-22 hours, a monomer mixture of 17% octylacrylate, 74% styrene, 8% of methyl half ester of maleic acid and 1%water together with additional emulsifying liquid consisting of 10%sodium lauryl sulfate solution, at about 5 parts by weight per hour, thetotal additions consisting of about 140 parts by Weight of monomer and100 parts by weight of emulsifier. About 15 hours after the start of thereaction the temperature is raised to 40 C. and, after all the monomeris added, the temperature is raised to about C. and the reaction mixtureheated for an additional period of about 2 hours, having addedadditionally 0.5 parts by weight of hydrogen peroxide catalyst. Ifdesirable there may be added an additional amount of aqueous dispersingagent such as a 12% sodium lauryl sulfate solution depending uponwhether a more or less viscous dispersion is desired. The product,prepared as described, is an aqueous latex containing colloidalparticles of an interpolymer of 48% styrene, 60% octyl acrylate and 2%of the methyl half ester of maleic acid.

A specific example of a latex especially suitable for use in the coatingor film-forming compositions of the present invention is astyrene-acrylic latex composed of a copolymer of styrene, octyl acrylateand one of the copolymerizable, ethylenically unsaturated organiccarboxylic acid compounds herein described, specifically a methyl,ethyl, or butyl acid (or half) ester of maleic acid.

Where the interpolymer or copolymer latices include an unsaturatednitrile, such copolymers may be prepared by the processes described inUS. Patent 2,767,153 granted October 16, 1956 to Ernest A. Sutton,assigned to Monsanto Chemical Company.

These latices'may also generally be obtained by interpolymerizing-themonomer components within a certain hereinbefore specified range ofproportions. The unsaturated ester usually comprises about 35-60% byweight of the total monomer charge, the unsaturated nitrile generallycomprises 310% by weight of the total monomer charge, the unsaturatedmonocarboxylic acid usually comprises about 2-5% by weight of the totalmonomer charge and the remainder of the monomer charge i.e. 6025% byweight is usually comprised of the monovinylidene hydrocarbon. Laticesprepared by interpolymerizing the monomeric components in the aboveproportions will, when employed in certain compositions of thisinvention, provide compositions which will dry to form continuous filmsat a temperature of about 10 C. or less. In a preferred latex about3545% by weight of unsaturated ester, 310% by weight of unsaturatednitrile, 3-5% by weight of unsaturated monocarboxylic acid and 6040% byweight of monovinylidene aromatic hydrocarbon may be interpolymerized toform latices which, when em ployed in the compositions of this inventionwill provide compositions which will dry to form continuous films at atemperature as low as 5.0 C. or less.

In the compositions which form the slip-resistant coatings of thisinvention, the quantity of colloidal silica as S10 may vary to someextent but is desirably in the range of 8% to 30% by weight andpreferably in the range of about 10% to 15% by weight. Additionally, theamount of colloidal silica as SiO is desirably in excess of 10 parts byweight per parts by weight of any of the aforedescribed copolyrnerspresent in the compositions employed to form theslip-resistant coatingsof this invention, and preferably in the range of about 25 parts to 250parts by weight of SiO' per 100 parts by weight of a particularcopolymer. If the amount of SiO;, is below 10 parts per 100 parts byweight of the copolymer, the films formed from such compositions willexhibit little if any soil resistant properties and will often be tacky.In general the upper limit of colloidal silica as SiO will be about 500,parts by weight per 100 parts by weight of the copolymer. If such limitis exceeded the films formed will tend to be discontinuous and suchfilms generally do not have good resistance to water penetration and donot act as moisture vapor barriers.

The compositions which are employed to form the slipresistant coatingsof this invention may be prepared in a variety of ways. For example, anaqueous latex of the copolyrner can be added directly to thealkali-stabilized colloidal silica aquasol and dispersed therein. Whenthe finely divided copolymer is added in the form of an aqueous latexhowever, it is preferred that such latex have at least 40% by weight ofthe copolymer dispersed therein in order to avoid excessive dilution ofthe aquasol.

The preferred compositions, for use to form the slipresistant coatingsthe present invention, are characterized in having a total dispersedsolids content, comprised of the copolymer and colloidal silica in totalamounts of from between 30% and 40% by weight, preferably 32% to 37% byweight, a viscosity (Brookfield) of between 6 and 14, preferably between7.5 and 12.5, centipoises at 25 C., and the dried coatings produced fromthese compositions have a specific gravity of from 1.3 to 1.9,preferably from 1.5 to 1.7, at 25 C. The preferred coating compositionsare further characterized in that the total solids content of thecopolymer and colloidal silica comprises a copolymer to Si'O Weightratio of from 4:1 to 1:4, preferably from 3:1 and 1:3. The coatingcomposition, which is particularly preferred from the standpoint ofoverall performance and versatility of the resulting coating, is acomposition having a total solids content (comprised of the copolymerand colloidal silica) of 34.6% by weight, wherein the weight ratio ofcopolymer to Si0 is about 1:1, and has a viscosity of 9.0 centipoises at25 C. The dried coatings produced fromsuch compositions have a specificgravity of about 1.82.

The thermoplastic resin or polymer sheets which may be madeslip-resistant in accordance with the present invention are fabricatedby processes well-known in the art such as for example by molding orextrusion processes. The thermoplastic polymer sheets which arefabricated 9 by molding processes are generally rigid or semi-rigid orflexible and usually have thicknesses of of an inch or greater, whereasthermoplastic polymer sheets which are fabricated by extrusionprocesses, are usually flexible and generally have thicknesses of from0.5 mil to of an inch. Such sheets may be transparent or translucent,depending upon the character of the thermoplastic polymer, and thesurface of such sheets is almost always extremely slippery and in anyevent is too slippery for many uses. Such thermoplastic polymers mayalso occur as sheets or films which have been sprayed on other sheetedmaterial, for example paper, and the thickness of such thermoplasticsheet is then usually less than 1 mil.

The coating compositions used in this invention may be employed toimpart slip-resistant properties to a wide variety of sheets or filmsfabricated from the hereinreferred-to thermoplastic resins or polymersor to cellulosic sheets such as paper which have on their outer surfacea coating or film of such thermoplastic resins or polymers. For example,the surfaces of molded or extruded sheets fabricated from polyvinylacetate, polyvinyl chloride, polystyrene, polyethylene, polypropylene,and the like, may be made slip-resistant when a coating of one of theaforedescribed liquid coating compositions is applied to such sheets andthe coating is dried, preferably by heating at a temperature in therange of from about 30 C. to just below the softening point of thethermoplastic or resin or polymer sheets. Also, .fiexible films whichhave been fabricated from the aforementioned thermoplastic resins orpolymers or dry thermoplastic resin or polymer films which are adheredto or on paper may be made slip-resistant when a coating of one of theaforedescribed liquid compositions of colloidal silica and copolymer isapplied to such films, and the coating is thereafter dried.

Although all of the aforementioned thermoplastic polymer-sheets r filmsmay be rendered slip-resistant when coated in accordance with theprocesses of this invention, the wide commercial acceptance ofpolyolefin films or sheets particularly polyethylene films or sheets, inaddition to certain physical and chemical properties of such films,render them especially suitable for treatment by the processes hereindescribed. Such polyethylene sheets, films and coatings are well-knownin the art and are preparedhy processes described on pages 411 to 417 ofHigh Polymers, volume XI, by R. A. U. Raff and J. B. Allis-on, publishedin 1956 by In-terscience Publishers, 250 Fifth Avenue, New York, NY. Thephysical and chemical properties and types of polyethylene films, sheetsand coatings which may be made slip-resistant in accordance with theprocess of the present invention are described on pages 447 to 471 ofthe above cited publication.

The polyolefin films, sheets and coatings which can be madeslip-resistant by the processes of this invention consist of highdensity resins or polymers, that is, for example, polyethylene resins orpolymers composed of large or high molecular weight molecules; lowdensity resins or polymers, that is, for example, polyethylene resins orpolymers composed of smaller or lower molecular weight molecules, andmixtures of these products. Such polyethylenes are characterized inhaving a density in the range of 0.910 to 0.960 gram per cubiccentimeter, a Melt Index determined as described in ASTM D 1238-57T inthe range of 0.2 to 8.0, a tensile strength determined as described inASTM D 412-51T of 1400 to 4400 pounds per square inch, an impactstrength determined as described in ASTM D 256-56 of from 0.7 to greaterthan 16.0 foot pounds and a hardness (Shore D) of from 44 to 70.

Such polyolefin films which may be made slip-resistant in accordancewith the processes of the present invention usually have a thickness offrom about 1.0 to about 20 mils depending on the way in which the filmis prepared or on the contemplated end use of the film. Where, forexample, the film has been prepared by spraying or rolling a solution ofa polyolefin, such as polyethylene, on a cellulosic sheet such as paperor cardboard, the film so produced usually has a thickness of less than1.0 mil. When the polyethylene film has been prepared by extrusion forgeneral packaging purposes for example, for fabrication into bags, suchfilm usually has a thickness in the range of from about 0.5 to about 20mils depending upon the weight of the material to be packaged. Formedium and light packaging, film thicknesses of the order of about 1.5to about 4 mils are ordinarily preferred.

The polyolefin films may be treated with the aforedescribed liquidcoating compositions of colloidal silica and the copolymer in a varietyof ways, for example, by spraying, brushing, or rolling. The resultantliquid coating may then be air dried or heat dried, but is preferablydried at a temperature in the range of from 50 C. to 75 C. The coatings,when dried may be continuous or discontinuous but are generallycontinuous, adherent films and may be clear or opaque depending upon thesize of the particles of SiO and the thickness of the coating or film.Generally the films will be transparent where the silica particles havean average particle size below millimicrons and will usually becomeopaque when the average size of the particles of Si0 is increased abovemillimicrons and the dried coating has a thickness of above 0.5 mil.Clear transparent coatings will almost always be obtained where thesilica particles have an average particle size below 30 millimicrons.The dried coatings usually have a thickness in the range of from 0.1 to1.0 mil and preferably contain between 20% and 71.5% by Weight ofcolloidal silica and between 80 and 28.5% by weight of the finelydivided interpolymer.

The polyolefin films or sheets, when coated as aforedescribed, are filmsand sheets which have excellent slipresistance wherein the tensilestrength, tear strength and impact strength is usually eithersubstantially the same or is slightly increased over the tensile, tear,and impact strengths of the untreated films or sheets.

The slip-resistant thermoplastic resin films of this invention may beused to fabricate containers such as bags which can then be used for thepackaging of foodstuffs, chemicals and the like. Such slip-resistantcontainers will generally not slip and slide against each other duringcommerical conditions of transport and usually can be stacked forstorage without danger of slippage and resultant injury to warehousepersonnel.

In FIGURE 2 of the accompanying drawings, wherein for the purpose ofillustration is shown still another preferred embodiment of thisinvention, the numeral 13 designates a transparent packaging containerwhich has four walls composed of transparent, flexible, thermoplasticpolymer (preferably polyethylene) film 12, sealed on two sides byclosures or (seals) 14, and having a thin, continuous coating 11 whichis transparent and adherent to film 12, and is composed, for example, ofa uniform mixture of colloidal particles of the aforementionedalkali-stabilized colloidal silica and interpolymer, for example, ofstyrene, alkyl acrylate and unsaturated carboxylic compound, preferablyderived from the aqueous latex of interpolymer. As in the case ofarticle 10 illustrated in FIGURE 1, the coating 11 on the container 13may be continuous or discontinuous but, in any event, providesslip-resistance for the container 13.

The packaging containers of this invention may be single wall ormulti-walled packaging containers. In the case of single walledpackaging containers such containers may be fabricated directly from thecoated thermoplastic polymer sheets of this invention or such containersmay be fabricated from uncoated thermoplastic polymer sheets to whichthe coating may be applied by brushing, spraying, or the like, after thepackaging container has been fabricated.

In the case of multi-walled packaging containers, such containers can befabricated using conventional methods and materials in which the outerlayer is composed of a thermoplastic sheet which has been madeslip-resistant in accordance with the processes of this invention. Alsomulti-walled plastic containers in which the outer layer or wall iscomposed of a cellulosic sheet material which has been coated with athermoplastic polymer such as, for example, polyethylene orpolypropylene, may be made slip-resistant by applying the slip-resistantcoatings of this invention to the polymer surface of the sheet eitherprior to or after it has been fabricated as the outer layer of apackaging container.

A further understanding of the composition, products, and processes ofthis invention will be obtained from the following specific exampleswhich are intended to illustrate the invention but not to limit thescope thereof, parts and percentages being by weight unless otherwisespecified.

EXAMPLE I One hundred parts of an aqueous latex containing about 60% ofwater and 40% of a finely divided dispersed co polymer consisting ofparticles of the interpolymerization product of a mixture of 48%styrene, 50% octyl acrylate and 2% of the methyl half ester of maleicacid and having an average particle siZe between 150 and 250 Angstroms,were added with agitation at room temperature (about 25 C.) to 133 partsof an alkali-stabilized colloidal silica aquasol having an Si content of30%, a pH of about 9.5, an SiO :Na O weight ratio of about 150:1, anaverage particle sizeof about millimicrons and a sodium sulfate contentof about 0.11% by weight, thereby forming a coating composition having atotal solids content (comprised of the aforedescribedinterpolymerization product and SiO of 34.6% by weight, a viscosity of9.0 centipoises at C., a specific gravity of 1.62 and wherein theinterpolymerization product and SiO were present in a weight ratio of1:1.

A 1.5 mil thick transparent sheet of polyethylene film was coated on oneside with the above composition, employing a laboratory coating machineto provide a liquid film, which when dried consisted of a film having athickness of about 0.5 mil of dried composition. The sheet was thenheated to about C. for about 5 minutes until it was dried, that is, freeof liquid. The coated side of the resultant sheet was characterized inhaving a high-gloss and excellent, slip-resistant properties, thedetailed slipresistant measurements being shown in Example IV herein.The coating was not tacky and did not reduce the transparency, tensilestrength or the impact strength of the polyethylene film. The unusedportion of the composition was labelled Composition A and set aside forfurther evaluation as described in Example IV.

EXAMPLE II Two hundred twenty-five parts by weight of theinterpoiymerization product latex describedin Example I was added withagitation, at room temperature, to parts by weight of the colloidalsilica aquasol described in Example I thereby forming an aqueous coatingcomposition having a total solids content (comprised of theinterpolyrnerization product and SiO of 36.4%, a viscosity of 12.5centipoises at 25 C., wherein the specific gravity of the dried film was1.32 and wherein the interpolymerization product and SiO were present ina weight ratio of about 3:1.

The above composition was applied to one side of a 3.5 mil thick,transparent sheet of polyethylene film from an applicator roll, as thesheet passed at-a rate permitting an even application of a film of thecomposition on the surface of the polyethylene sheet, after which thepaper was continually passed through a drying zone at 60 C. The liquidcoating thickness was such that when the coating was dried it had athickness of 0.6 mil. The dried, coated polyethylene film so obtainedwas transparent and noni2 tacky, and was also characterized in havingexcellent slipresistance and a high-gloss finish.

The coated sheet was not tacky and had a slight increase in tensile andimpact strength over the uncoated poly ethylene sheet. The unusedportion of the composition was labelled Composition B and was set asidefor further testing with respect to slip-resistance as hereinafterdescribed in Example IV.

EXAMPLE Illv One hundred parts by weight of the interpolymerizationproduct latex described in Example I was added with agitation, at roomtemperature, to 400 parts by weight of the colloidal silica aquasoldescribed in Example I to provide a composition having a total solidscontent (comprised of the interpolymerization product and SiO of 32.5%by weight, a viscosity of 7.5 centipoises at 25 C., and wherein thespecific gravity of the dried film was 1.85 and wherein the weight ratioof interpolymerzation product to silica was a weight ratio of 1:3.

The above described composition was applied to a sheet of polyethylenefilm of the same thickness as in Example I using the same method ofapplication and drying as described in that example. The. resultingsheet had a high gloss and was slip-resistant on the coated side. Thesheet was also transparent and the liquid coating applied was such thatwhen it was dried the resultant dry coating had a thickness of about 0.2mil. The dried coating was not tacky and did not reduce the tensilestrength or the impact strength of the polyethylene sheet. The remainderof the above described composition was labelled Composition C and setaside for evaluation of slipresistance of polyethylene film coatedtherewith.

The dried films or coatings of compositions A through C inclusive, arecharacterized in having excellent slipresistance as will be seen fromthe following.

EXAMPLE IV Composition Used Uncoated Control Angle of Slip (Degrees) 17.7 33. l 35. 1 35. 0 Percent Increase in Angle of Slip 0 86. 9 9.81 97. 7

The angle of slip, which is a direct indication of slipresistance isdetermined as follows:

An adjustable inclined lplane having a fixed glass plate fastenedthereto and equipped with an angle measuring scale is used as a testingdevice; a sheet of the polyethylene film, either the control or one ofthe treated sheets, is fastened in a suitable manner to the fixed glassplate; and a second sheet of polyethylene film, treated in the samemanner, is mounted on a glass plate which is free to slide on the fixedglass plate. The sheet of polyethylene film and glass plate are mountedon the polyethylene covered fixed glass plate when the latter is in ahorizontal position and then weighted wth a gram weight. The angle ofthe inclined plane. is gradually and slowly increased until the movaibleweighted sheet of polyethylene film begins to slide or move down theinclined plane. The angle so determined is the angle of slip. Incarrying out the above tests, the glass plates of the testing devicewere covered with the same treated or untreated polyethylene sheet.

The dried films or coatings of com-positions A through C, inclusive, aresmooth, continuous, clear and transparent. They are furthercharacterized in being nontacky and in having high gloss and goodslip-resistance.

The coatings formed by compositions A and B also have excellentflexibility and such coatings are excellent for use when it is desiredto fold or bend the polyethylene sheets, since the coating will notbreak, crack, flake off, or otherwise lose its continuity on the treatedpolyethylene sheet.

When the surfaces of polyethylene sheets were coated with thehereinbefore described styrene-acrylic latices per se, the coatings wereextremely tacky and adhered to untreated sheets when placed in contactwith such sheets.

When the polyethylene sheets were coated with colloidal silica aquasolsper se, the resultant coated sheets exhibited no slip-resistance. Sinceit is known that cellulosic sheets such as paper and rboxboard may berendered substantially slip-resistant when such coatings are applied, itis apparent that there is no adhesion of the colloidal silica per se tothe polyethylene sheet, or to the other slipping thermoplastic polymersheets referred to.

EXAMPLE V One hundred parts by weight of a stable homogeneous aqueouslatex containing about 50% water and 50% of a finely divided dispersedcopolymer consisting of the interpolymerization product of a mixture of52% styrene, 40% 2-ethylhexyl acrylate, 2% methacrylic acid and 6%acrylonitrile and having an average particle size of between about 0.2and 0.3 micron were added, with agitation at room temperature (about 25C.), to 133 parts by weight of the colloidal silica aquasol described inExample I thereby forming a composition having a total solids content(comprised of 'the copolymer and Si'O of 38.6%, a viscosity of 7.5centipoises at 25 C. and a specific gravity of 1.14 wherein thecopolymer and SiO were present in a weight ratio of 1.25:1.

The above composition was divided into three separate aliquots whichwere respectively diluted with water to provide compositionshaving-respective total solids levels of 7.5% and 10% by weightrespectively but having the same ratio of copolymer to SiO A 1.5 'milthick transparent sheet of polyethylene film was coated on one side withthe composition containing 5% total solids, employing a laboratorycoating machine to provide a liquid film which, when dried, consisted ofa film having a thickness of about 0.5 mil of dried composition. Thesheetwas then heated at about 50 C. for about 5 minutes until it wasdried, that is, free of liquid. A second 1.5 mil thick transparent sheetof polyethylene film was coated on one -side with the compositioncontaining 7.5% by'weight of total solids as above described to producea'polyethylene film having a dried 0.6 mil thick coating. A third 1.5mil thick transparent sheet of polyethylene was coated as abovedescribed with the composition containing 10% by weight of solids toproduce a dried coating having a thickness of 0.7 mil. The. coated'sidesof all three of the polyethylene sheets werecharacterized in having ahigh gloss and excellent slip-resistant properties. The quantitativeslip-resistance measurements are shown in Example VI herein. Thecoatings were not tacky and did not reduce the transparency, tensilestrength. or the impact strength of thepolyethylene film. The coatedside of the polyethylene films also exhibited excellent soil releasingand soil-retardency properties when compared with untreated polyethylenefilm.

EXAMPLE v1 The coated transparent polyethylene sheets of Example V wereevaluated for improvement in slip-resistance of frictioniza-tion by themethod described in Example IV. The following table shows theimprovement in slipresistance of the treated sheets of polyethylene filmcompared with an untreated control sheet.

The procedure of Example V was repeated using the compositions describedin Example V except that the compositions were applied by means of aspray atomizer, to separate 3.5 mil thick transparent sheets ofpolyethylene film to provide polyethylene sheets having discontinuousfilms of respective coating compositions containing 5%, 7.5% and 10% byweight of solids wherein the weight ratio of copolymer to SiO was1.25:1.

The coated sides of the three polyethylene sheets were characterized inhaving high gloss and excellent slip-resistant properties. Additionallythe coated sides exhibited excellent soil-resistant and soil retardencyproperties when compared with an untreated polyethylene sheet of thesame thickness. The coatings were not tacky and did not reduce thetransparency, tensile strength or impact strength of the polyethylenefilm.

Slip-resistance measurements conducted as in Example VI demonstratedthat these coated films had substantially the same improvement inslip-resistance over similar untreated polyethylene sheets as thetreated polyethylene sheets of Example V (e.g."l.5 mils thick) had overthe untreated polyethylene sheets of that example.

EXAMPLE VIII Three separate compositions were prepared as follows:

An alkali-stabilized colloidal silica aquasol containing 30% by weightof SiO having an SiO :Na O weight ratio of about :1, a sodium sulfatecontent of about 0.1% by weight and containing particles of colloidalsilica having an average particle size of about 40 miliimicrons andparticle sizes in the range of from about 35 to 50 millimicrons wasadded to an aqueous latex containing about 53% by weight of water and47% by weightof a finely divided dispersed copolymer consisting of theinterpolymerization product of a mixture of 52% styrene, 40% 2-ethylhexyl acrylate, 2% methacrylic acid and 6% acrylonitrile. Thefinely divided particles of the interpolymerization product had anaverage particle sizeof between 2000 and 3000 Angstroms. The silicaaquasol and latex were mixed with agitation at room temperature (about25 C. in the proportions (parts by weight) listed below).

The'coatings so produced had the following physical char.- acteristicsTotal Polymer- Specific Viscosity,

Composition Solids SiO Ratio Gravity 25 C.

Three separate aliquot samples of composition 1 were diluted with wateruntil they respectively contained 5%, 7.5 and 10% by Weight of totalsolids but had a polymer-SiO weight ratio of 2: 1. The diluted sampleswere applied to separate polyethylene sheets having a thickness of 6.5mils by means of an atomizer to form discontinuous coatings thereon. Thepolyethylene sheets were dried overnight in air at a temperature of 72F. and a relative humidity of 50%.

All of the dried coated films were transparent and were chacterized inhaving excellent slip-resistance and a hgh gloss finish. The films whichhad been coated with composition 1 containing 10% by weight of totalsolids exhibited a very slight tackiness and were not quite as soilresistance as the other coated films which exhibited fair to goodsoil-resistance. However, the films coated with the compositionscontaining 10% by weight total solids showed almost a 100% improvementin slip-resistance when compared with similar untreated polyethylenefilms. The coatings did not reduce the transparency, tensile strength orimpact strength of the polyethylene films.

Three separate aliquot samples of composition 2, having a polymer-SiOweight ratio of 1:1, were diluted with water until the samplesrespectively contained 5%, 7.5% and 10% by weight of total solids buthad a polymer- Si weight ratio of 1:1. The diluted samples were appliedto separate polyethylene sheets having a thickness of 3.5 mils by meansof an atomizer to form a continuous coating thereon. The polyethylenesheets were dried overnight in air at a temperature of 72 F. and arelative humidity of 50%.

All of the dried coated films were transparent and were characterized inhaving excellent slip-resistance and a high gloss finish. All of thefilms were non-tacky and exhibited excellent soil-resistance andsoil-retardency properties. In no instance did the coated films exhibita reduction in transparency, tensile strength, or impact strength.

Three separate aliquot samples of composition 3, having a polymer-SiOweight ratio of 1:2 were diluted with water until the samplesrespectively contained 7.5% and by Weight of total solids but had apolymer- SiO weight ratio of 1:2. The diluted samples were applied bymeans of a laboratory coating machine to separate polyethylene sheet-shaving a thickness of 6.5 mils to form continuous liquid coatingsthereon. The coatings varied in thickness after drying depending uponthe total solids content of the respective composition, from 0.5 mil to0.7 mil. The polyethylene films were dried overnight 2}; temperature of72 F. and a relative humidity of All of the dried coated films weretransparent and were characterized in having excellent slip-resistanceand a good gloss finish. In no instance was there an adverse effect onthe tensile strength or impact strength of the film to remove thecoating therefrom. Adhesion was evaluated as excellent when the Scotchtape substantially failed to remove the dried coating compositions fromthe polyethylene film.

Soil resistance and/or soil-retardency was measured using the methoddescribed on page 156 of volume 27 of the Journal of the American OilChemists Society and consisted of blowing a synthetic soil on the coatedsurfaces of the polyethylene films and observing the amount of coilretained on and adhering to such surfaces.

In general, coating compositions having a polymer- SiO weight ratio of1:1 produced coated films having the best and most nearly balancedcombination of slipresistance, soil resistance and adhesive properties.Coating compositions having a polymer-$0 weight ratio of 2:1 to 4:1while having excellent slip-resistant properties are also soil-resistantcompared to untreated films but are not quite as soil resistant as filmscoated with compositions having polymer-SiO weight ratios of 1:1 and1:2. On the other hand polyethylene films coated with compositionshaving a polymer-SiO weight ratio of 1:2 to 1:4, while having excellentsoil resistant properties and while having improved slip-resistance whencompared with untreated polyethylene films are not as slip-resistant asfilms coated with compositions having a higher SiO to polymer ratio.

It is to be understood that coating compositions containing up to 40% byweight of total solids may be used to form the coatings on the coatedpolyolefin films of this invention. However, uniform coatings aregenerally most readily obtained when the compositions contain from 5% to10% by weight of total solids as compared to a total solids content inexcess of 10% by weight.

What is claimed is:

1. A transparent packaging container characterized by a slip-resistantsurface and having side walls and a top and bottom closure composed ofan outer thermoplastic polymer film layer, said thermoplastic polymerlayer having a normally slippery outer surface and a slip resistant,smooth, non-tacky film on said surface and adherent thereto, which filmis composed of a uniform mixture of particles of an alkali stabilized,colloidal silica and particles of a finely divided copolymer comprisingthe interpolymerization product of (1) from'albout 26% to about of amonovinylidene aromatic hydrocarbon, (2) from about 60% to about 34.5%of an alkyl ester of an unsaturated acid selected from the groupconsisting of acrylic acid and methacrylic acid and (3) from about .5%to about 14% of an ethylenically unsaturated organic carboxylic compoundhaving at least one carboxyl group and copolymerizable with saidmonovinylidene aromatic hydrocarbona'nd said alkyl ester; the quantityof colloidal silica and interpolymerization product in said adherentfilm being in the range of from 10 to 500 parts by weight of. SiO perparts by weight of said interpolymerization product.

2. A transparent packaging container characterized by a slip-resistantsurface and having side walls and a top and bottom closure composed ofan outer thermoplastic polymer film layer having a normally slipperyouter surface and a slip resistant, smooth, non-tacky film on saidsurface and adherent thereto, which film is composed of a uniformmixture of particles of an alkali stabilized, colloidal silica andparticles of a finely divided interpolymer of from about 26% to 65% byweight of styrene, from about 60% to 34.5% by weight of an alkylacrylate, and from about 0.5% to 14% by weight of an ethylenic-allyunsaturated organic earb-oxylic compound containing from 3 to 9 carbonatoms and having at least one carboxyl group and copolymerizable withsaid styrene and said alkyl acrylate; the quantity of colloidal silicaand interpolymer insaid adherent film being in the range of from 10 to500 parts by weight of SiO per 100 parts by weight of said interpolymer.

3. A transparent packaging container characterized by a slip-resistantsurface and having sidewalls and a top and bottom closure composed of anouter polyethylene layer having a normally slippery outer surface and aslip resistant, smooth, non-tacky film on said surface and adherentthereto, which film is composed of a uniform mixture of particles of analkali stabilized, colloidal silica having an Si0 to Na O weight ratioof from about 10:1 I0 abo t 500:1 and an average particle size of about5 to about 80 millimicrons, and particles of a finely dividedinterpolymer of from 30% to 48% by weight of styrene, from 69.5 to 38%by weight of octyl acrylate and from 0.5% to 14% by weight of anethylenically unsaturated organic carboxylic compound containing from 3to 9 carbon atoms and having at least 1 carboxyl group andcopolymerizable with said styrene and said octyl acrylate, the particlesof said interpolymer having a particle size between about 150 and 250Angstr-oms; the quantity of colloidal silica and interpolymer in saidadherent film being in the range of from 25 to 250 parts by weight of Siper 100 parts by weight of said interpolymer.

4. A transparent packaging container characterized by a slip-resistantsurface and having side walls and a top and bottom closure composed ofan outer thermoplastic polymer film layer having a normally slipperyouter surface and a slip-resistant, smooth, non-tacky film on saidsurface and adherent thereto, which film is composed of a uniformmixture of particles of an alkali stabilized, colloidal silica andparticles of a finely divided copolymer consisting essentially of theinterpolymerization product of (1) from about 25% to about 60% of amonovinylidene aromatic hydrocarbon, (2) from about 60 to about 35% ofan alkyl ester of an unsaturated acid selected from the group consistingof acrylic acid and methacrylic acid, (3) from about 5% to about 20% ofan ethylenically unsaturated organic carboxylic compound having at leastone carboxyl group and copolymerizable with said monovinylidene aromatichydrocarbon and said alkyl ester, and (4) from about to about 3% of anunsaturated nitrile; the quantity of colloidal silica andinterpolymerization product in said adherent film being in the range offrom about 10 to 500 parts by weight per 100 parts by weight of saidinterpolymerization product.

5. A transparent packaging container characterized in having aslip-resistant surface and having side walls and a top and bottomclosure composed of an outer polyethylene layer having a normallyslippery outer surface and a slip-resistant, smooth, non-tacky film onsaid surfface and adherent thereto, which film is composed of a uniformmixture of particles of an alkali stabilized, colloidal silica having anSiO to Na O Weight ratio of about 10:1 to 500:1 and an average particlesize of about 5 to about 80 millimicrons and particles of a finelydivided interpolymer of from about to by weight of styrene, about 45% to35% by weight of Z-ethylhexyl acrylate, from about 5% to 2% by weight ofmethacrylic acid, and from about 10% to 3% by weight of acrylonitrile,said inter-polymer being characterized in having an average particlesize of from about 1000 to 5000 Angstroms; the quantity of colloidalsilica and interpolymer in said adherent film being in the range of fromabout 25 to 250 parts by weight per parts by weight of saidinterpolymer.

References Cited by the Examiner UNITED STATES PATENTS 6/1953 Wilson229--53 10/1959 Wolinski 117--l6

1. A TRANSPARENT PACKAGING CONTAINER CHARACTERIZED BY A SLIP-RESISTANTSURFACE AND HAVING SIDE WALLS AND A TOP AND BOTTOM CLOSURE COMPOSED OFAN OUTER THERMOPLASTIC POLYMER FILM LAYER, SAID THERMOPLASTIC POLYMERLAYR HAVING A NORMALLY SLIPPERY OUTER SURFACE AND A SLIP RESISTANT,SMOOTH, NON-TACKY FILM ON SAID SURFACE AND ADHERENT THERETO, WHICH FILMIS COMPOSED OF A UNIFORM MIXTURE OF PARTICLE SOF AN ALKALI STABILIZED,COLLOIDAL SILICA AND PARTICLES OF A FINELY DIVIDED COPOLYMER COMPRISINGTHE INTERPOLYMERIZATION PRODUCT OF (1) FROM ABOUT 26% TO ABOUT 65% OF AMONOVINYLIDENE AROMATIC HYDROCARBON, (2) FROM ABOUT 60% TO ABOUT 34.5%OF AN ALKYL ESTER OF AN UNSATURATED ACID SELECTED FROM THE GROUPCONSISTING OF ACRYLIC ACID AND METHACRYLIC ACID AND (3) FROM ABOUT .5%TO ABOUT 14% OF AN ETHYLENICALLY UNSATURATED ORGANIC CARBOXYLIC COMPOUNDHAVING AT LEAST ONE CARBOXYL GROUP AND COPOLYMERIZABLE WITH SAIDMONOVINYLIDENE AROMATIC HYDROCARBON AND SAID ALKYL ESTER; THE QUANTITYOF COLLOIDAL SILICA AND INTERPOLYMERIZATION PRODUCT IN SAID ADHERENTFILM BEING IN THE RANGE OF FROM 10 TO 500 PARTS BY WEIGHT OF SIO2 PER100 PARTS BY WEIGHT OF SAID INTERPOLYMERIZATION PRODUCT.